Acoustic reservoir for use in a magnetic sound recording and reproducing system



July 29, 1947. F. RIEBER 2,424,633

' ACOUSTIC RESERVOIR FOR USE IN A MAGNETIC SOUND RECORDING AND REPRODUCING SYSTEM Filed.May 19, 1944 INVEATIOR.

45 6 r ANKREBER T15-Z BY 6 ATTORNEY.

Patented July 29, .1947

AdOUSTIC RESERVOIR. FOR USE IN A MAG- NETIC SOUND RECORDING AND REPRO- DUCING SYSTEM Frank Richer, New York, N. Y., assignor to Interval Instruments, Inc., New York, N. Y., a corporation of New York Application May 19, 1944, Serial No. 536,407

This invention relates to an electrical recording apparatus designed for the recording of electrical impulses in a form in which they may be later reproduced automatically at short predetermined intervals and, also in some of its aspects, to a device in which a plurality of such impulses may be recorded in timed sequence, so that at any subsequent period of time desired the timed relation of those signals may be determined.

Such apparatus in itself has many uses, for example, in signaling systems in which electrical impulses may be sent out over different electrical channels having a significant time relationship, so that the recording of the time, as well as the impulse, is important.

In one of its important aspects, this invention may be used as an acoustic reservoir in which microphones are used to produce the electrical quantities to be recorded, thereby producing a sound record which, whenever desired, may be reproduced with fidelity and which may in this manner be reproduced in fixed time relation to the original sound which actuated the microphone.

It is an object of this invention to provide a continuous record surface free from discontinuities or variations which would introduce noises which might obscure or mask the signals or sounds to be recorded, and which will record the impulses faithfully, and yet which may be readily wiped clean for another recording when desired.

It is possible to build a delay circuit entirely from electrical factors, avoiding the need of converting the energy from electrical to acoustic form and back again, but such circuits are difficult and expensive to construct, and if theltotal delay is more than a very brief time, they become prohibitively expensive. Moreover, such electrical delaying devices tend to respond unequally at different frequencies, so that all sounds in the frequency range are not transmitted with equal fidelity. Such systems, moreover, are not practical from another point of view in many instances in which it is desirable to make the interval of delay adjustable within a considerable range.

Devices for producing such records mechanically have been proposed, which have served for some purposes, but they have embodied limitations that for many other purposes have been serious. The reproduction of sound upon photographic film possesses the serious limitation that it is not feasible to employ a continuous film and to wipe the film clean of the record in condition for another recording. It is also impractical to produce such a system with the usual type of phonograph disc, as it is not practical to wipe i! 6 Claims. (Cl. 179100.2)

the record at will to prepare for new recordings.

It has also been proposed to produce such a record by producing local magnetization of a magnetic material. Such magnetic recording has, however, in obtaining the continuous recordbearing surface, heretofore been subject to several limitations of a structural nature.

Proposals to use rotating discs of magnetic material possess the limitation that sheet metal from which the discs are made varies in molecular structure, in that it is distinctly fibrous in the direction in which the metal was rolled and correspondingly molecularly discontinuous transverse to that direction. This difference, for most structural purposes, is not material, but it is distinctly disadvantageous in the magnetic reproduction of sound, because the variation in internal structure causes a variation in the magnetic properties of the disc. Twice during each revolution the reproducer or recorder is moving longitudinally of the fibres, in which direction the maximum magnetization can be made, without appreciable moleculardiscontinuity; but twice also the reproducer or recorder must move across the fibres, in which direction magnetization is more difiicult and in which, moreover, a discontinuity exists probably between fibres or between groupsof fibres, which results in a burst or rush of noise of appreciable volume.

Such a disc, therefore, creates a noise twice for each revolution, which seriously interferes with the recording and reproducing of the desired sound. Such noise is important from another point of view, in that there is a practical limit to the volume of the signal sound that can be produced with any given apparatus; and with a high maximum noise level, many uses of the device are impaired and many others precluded. Such a disc is distinctly disadvantageous from another point of view whenever it is desired to have more than a short length of time between reproductions, because of the limitations in the practical diameter of the discs.

Similar difficulties are encountered in utilizing sections of steel tubing as a continuous record, since the fibres of such tubing extend in the direction in which the tubing was drawn, that is, parallel to the axis, and hence if We use the cylindrical surface of a section of such tubing for a recording medium, the recording and reproducing elements will, at all times, be traveling transverse to the grain of the tubing. This, as has been previouslyshown, is the condition for the highest noise level and the greatest irregularity.

It has also been proposed to construct a contimlous recording surface by Welding the ends of a steel tape or wire together to make it continuous. Steel tape or drawn wire is itself a desirable material, as the fibres all extend in the direction of extension of the wire or tape, and therefore afford the minimum of discontinuity in that direction. When such materials, however, are welded together at the ends, this continuity is broken at the weld, and once in each revolution this discontinuity produces abrupt changes in the reproduced sound, which for many purposes are quite objectionable. The weld, moreover, has distinctly different mechanical properties from the remainder of the tape or wire, and the constant travel of the recording and reproducing apparatus over this weld line introduces undue and undesirable wear upon them.

As between a wire and a tape, experience shows that when it is desired to produce local magnetization for such purposes as sound recording, that the record is more efficiently retained upon a wire or narrow tape than upon a tape of appreciable width.

It is an object of this invention to overcome these limitations and to produce a record surface and an apparatus having a record surface which possesses the advantages of the drawn wire in its uniformity and low noise level, which is at the same time free from disturbances due to welding, and moreover to produce a record having the strength of signal customarily associated with a band of material width while having the permanence of signal of a single wire.

It is a further object to produce a system by which we may definitely and accurately control the time interval between the recording of the sound and its reproduction, that is, by which the sound may be automatically reproduced, a predetermined and controllable time interval after the sound is received.

The invention accordingly comprises a device possessing the features, properties and the relation of elements which will be exemplified in the article hereinafter described and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of a device embodying this invention, the elements of the apparatus being separated more clearly to show the construction.

Fig. 2 is a sectional view of the recording magnet.

Fig. 3 is a diagrammatic section through the record cylinder,

Fig. 4 is a sectional view of the reproducing magnet and its supporting mechanism.

The instrument in the drawings represents an assemblage of three acoustic reservoirs all alike in construction, so that the description of one applies to all. The three are here assembled, because in many uses of the device a plurality of said elements, coordinated together, is required. For convenience, we have described the construction of, and have applied reference numerals to, the elements of one of these devices only, while to the corresponding elements of the other devices we have applied the same reference numerals with the subscripts a and respectively. The record surface itself comprises a cylinder 20 having wound upon its outer surface a plurality of turns of a magnetic wire 2|, the adjacent turns of which (see Fig. 2) are either in contact or only 4 slightly spaced from each other, so that the maximum number of turns may be in cooperative relation to the recording and reproducing poles, as will be hereinafter described. The ends of this wire are attached to the cylinder in any convenient manner, and the width of the winding is greater than the width of the poles hereinafter described. For some purposes I prefer to grind off the surface of the wire turns after they have been wound on the cylinder, as shown in Fig. 2, to give a more or less fiat exterior to provide the minimum of reluctance between the magnet poles and the wire.

These cylinders 20 are all mounted on a common shaft 22 journaled in uprights 23 carried by a base 24, and a constant speed motor, such as a synchronous motor 25, is connected to drive the shaft and the cylinders one revolution during the interval which it is desired to have elapse between the periodic reproductions of the sound.

Journaled upon the shaft 22 for each record cylinder is a ring member 26 completely surrounding the shaft and having upon one side thereof a projection 28 extending only partway around the circumference. This ring member is supported and held against rotation about the axis of the shaft 22 in any convenient manner, as for example by pins 30 extending through the ring members parallel to the shaft. Carried within the projection 28 is a recording magnet 33. This magnet, like the play-back and wiping magnets hereinafter described, is illustrated only schematically in Fig, 1. Its construction is shown in detail, however, in Figs. 2, 3 and 4. The magnet comprises a central core 34 surrounded by a coil of wire 35, the core having a chisel shaped point, as shown at 36, preferably having rounded ends 31 to minimize the discontinuity when a wire passes from under the magnet. lhe coil 35 is enclosed in a magnetic shell 38 extending On the outside down almost to the line of the chisel point 36 to furnish a return magnetic circuit.

The magnet 33 is supported with the chisel point 36 in light contact with the outer surface of the wire 2|, and as will be seen in Figs. 2 and 3, the core and the coil and the shell are elongated in shape transverse to the direction of the extension of the wire 2|, so that the chisel point will cooperate with a number of turns of the wire 2|.

Mounted within the other side of the projection 28 is a magnet 40 having a construction generally similar to the magnet 33, except that it is larger and having greater power and its pole piece is flat in shape, as shown at 4|, instead of being brought to a chisel point, or it is curved to correspond to the curvature of the recording surface itself. It is wide enough, that is, it extends a sufficient distance along the record surface in the direction of its movement, to destroy any record that may have been made thereon, whenever the magnet 40 is energized.

The inner surface of the ring member 26 is provided with a V-shaped annular groove 43, in which there is carried a spring split ring member 44 having a bracket 45, on which is carried a reproducing magnet 46 similar in construction to the magnet 33 previously described. In this manner the split ring 44 serves as a bearing to permit the magnet 46 to be moved about the axis of the shaft to change its angular position with reference to the recordin magnet 33, and hence to alter the time between the recording and the reproducing of the sound.

Means are provided to shift in an angular direction the split ring 44 and with it reproducing magnet 46. To accomplish this result, a groove 49 is cut around the member 26 in which there slides a wire 56 which is carried around a post 5| controlled by a knob 52. The magnet 46 is connected to the wire 50 by an arm 53 which also provides an indicator 54 moving over a dial 55.

It will be understood that the magnets 40- and 46 are, like the magnet 33, in registry with the wire surface. These magnets, however, are spaced from the wire. The circuits of these different reservoirs are identical in construction so that the parts will be described in connection with one of these devices and the corresponding parts in the other devices will be given similar numbers with the subscripts as previously described. The numeral 59 represents a microphone connected to the ground at 60, as shown, and at the other end to a pole 6| of a switch 62, the movable arm 63 of which is connected to the primary 64 of a transformer 65, the other side of the primary being connected to the ground at 61.

The high tension side of the secondary 68 of this transformer is connected to the grid 69 of an amplifier l0, and the low tension side is connected to the ground at H, it being understood that if the particular tube employed requires a grid bias, that such grid bias 'will be inserted in this circuit, being here represented by a battery 12. Another pole 13 of switch 62 is in position to be contacted with the arm 63 in its upper position, and this pole is connected by a wire 14 to the magnet 46, the other side of the magnet being connected to ground at 15. Thus the member 63 serves to connect the grid 66 of the tube either with the microphone 60 or with the reproducing magnet 46 at will.

The cathode of the amplifying tube 16 is connected to ground in the usual manner, and the plate 16 of this tube is connected to a battery i1 by-passed b a condenser 71a through the primary 18 of a transformer 19, the secondary 80 of which is connected to the movable arm 8| of a switch 82. One pole 83 of this switch is connected to the coil 35 of recording magnet 33, the other pole 84 of this switch being connected to whatever device is intended to utilize the reproduced sound, here shown as a loud speaker 85.

The wiping magnets 46 are connected in multiple and are operated by a battery 86 under control of a manual switch 81.

With the above record cylinder, records may be made magnetically upon the continuous surface, using at all times the most favorable conditions of metal structure, without introducing noises from cross-grain movement or from surface discontinuities. Such a record can be readily made, repeatedly reproduced at will, and then wiped out with uniformity and simplicity.

The device of this invention may be used for any purpose in which an acoustic reservoir is desired. In some instances incoming electrical waves may be fed directly to the recording magnets 33 and the wave may then be reproduced after any predetermined period of delay by the reproducing magnets 46, it being understood that the microphones and the loud speakers herein illustrated are symbolic only of a source of electrical waves and an instrumentality for utilizing the reproduced delayed wave respectively. For example, signals from separate channels may be fed to the respective magnets 33 and the same signals may be reproduced with a different time relationship.

Or sounds issuing upon a stage may be re produced in loud speakers remote from the stage synchronously with the arrival of the sound throughthe air at the remote point.

Moreover, since the movements of the magnet 46 is arneasure of the time delay between the signals, it will be evident that the time relationship between different signal sources may be determined by feeding those separate signals to the separate magnets 33 and then adjusting the respective magnets 46 to bring the reproductions into harmony and measuring the relative angular position of those magnets.

Since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A recording reproducing system including a member having a ferrous wire wound in a plurality of turns in a helical path, and a magnet mounted in position to cooperate with said ferrous wire having a chisel shaped pole face broad enough to overlie a plurality of said turns and means for rotating said member.

2. A recording reproducing system including a member having a ferrous wire wound in a plurality of turns in a helical path, and a magnet mounted in position to cooperate with said ferrous wire having a chisel shaped pole face broad enough to overlie a plurality of said turns, said pole face having its edges rounded away from said Wire.

3. An acoustic reservoir comprising a cylindrical member, a ferrous wire wound helically in a plurality of turns upon, and firmly attached to the surface of said cylindrical member, means for driving said cylindrical member at a constant speed, a recording magnet and a reproducing magnet, each having a pole face constructed to engage a number of turns of said wire and being mounted in a position to cause said pole face to cooperate with said wire, and means for moving said magnets relative to each other about the axis of the shaft.

4. A recording system for electromagnetic impulses, comprising a member having a cylindrical surface, a plurality of turns of a magnetizable wire wound helically upon said surface, a magnet having a chisel shaped pole face mounted adjacent to said wire, and having a length measured along the axis sufficient to cooperate with a plurality of turns of said wire.

5. A device in accordance with claim 4 in which the chisel shaped magnet has its ends slightly rounded away from the magnetizable wire.

6. An acoustic reservoir comprising a frame, a cylindrical member having a magnetizable wire wound helically upon its surface in a plurality of turns and firmly attached thereto, to form a magnetizable surface with a molecularly circumferentially continuous and homogeneous structure,

The fol file of th pole being broad enough to bridge across a plu- 5 rality of turns of said wire, a support mounted for rotation in said frame about said axis, and a second and similar magnet carried by said support whereby the relative angular positions of said magnets may be varied at will.

FRANK RIEBER.

Number REFERENCES CITED lowing references are of record in the is patent:

UNITED STATES PATENTS Name Date Pedersen May 2, 1905 Lieb Mar. 17, 1908 Begun Aug, 24, 1943 Goldsmith July 18, 1944 Egerton Jan, 11, 1921 

